Vibratory signaling device



Sept. 30, 1958 A. P. BoYsEN, JR., ET AL 2,854,542

VIBRTORY SIGNALING DEVICE Filed May 24, 1955 2 Sheets-Sheet 1 A. P.BOVSEN, JR. /NVENTORS E KREBS A TTOR/VEV sept. 3o, 195s A. P. BQYSEN,JR., ET AL VIBRATORY SIGNALING DEVICE 2 Sheets-Sheet 2 Filed May 24,1955 NE TW OPK EQUAL /ZEP PLucK//ve MAGNET-j A. f? BOVSEM JR. /NVj/TORSLf. KREBS A77'OPNEV United States Patent @thee Patented Sept. 30, 1958VEBRATORY SIGNALING DEVICE Albert P. Boysen, Jr., Basking Ridge, andLuther E. Krebs, West Grange, N. J., assignors to Bell TelephoneLaboratories, incorporated, New York, N. Y., a corporation of New YorkApplication May 24, 1955, Serial No. 510,634

Claims. (Cl. 20G- 87) This invention relates to vibratory signalingdevices, and particularly to devices of the type wherein a flexiblemechanical member or reed is set into vibration to generate anelectrical signal of characteristic frequency.

Telephone signaling systems have been developed wherein combinations ofalternating current of different frequencies are generated at thecalling subscribers subset and sent over the line to the central officeto establish the digit code of the called telephone number in thecentral office register-sender. A system of this kind is that shown inPatent 2,237,742, issued to A. A. Lundstrom on April 8, 1941. Togenerate the alternating cur rent, subsets have been developed whichinclude a number of vibratory reeds and keys. Each key, when depressed,plucks particular ones of the reeds. Each reed is disposed in a magneticfield and is surrounded by a pickup coil. When any reed is plucked itvibrates at its natural frequency, and produces in its coil analternating current of the same frequency. A generator of this kind isshown in Patent 2,147,710, issued to R. F. Mallina on February 2l, 1939.In a particular embodiment shown in that patent, ten keys and ve reedsare provided, each tuned to a different frequency. Each keysimultaneously plucks a particular combination of two of the reeds so`that ten frequency combinations are available corresponding to the tendigits on a telephone dial.

In utilizing frequency generators of this kind, it has been found thatwear of the reeds at the point where they are plucked by an actuationgpawl eventually causes changes in their natural frequencies. Since thecentral office equipment comprises frequency channels tuned to thefrequencies of the reeds in the subset, this necessitates frequent reedadjustment. Various attempts to reduce reed wear have been made. One ofthese is shown in Patent 2,352,723, issued July 4, 1944, to R. F.Mallina wherein mechanical means hold lthe reed pretensioned beyond itspoint of release by a key. However, it is still necessary for a latchingmember to hold and then slide off the end of the reed.

It is an object of the present invention to provide means for vibratinga flexible mechanical member without producing frictional wear of themember.

A further object is to provide a vibratory signaling device wherein areed is set into vibration without any wear producing physical Contactwith the actuating means and wherein the actuating means has no dampingeffect on the reed after having initiated the vibration.

According to the invention, a flexible ferromagnetic reed is cantileversupported with its free end bridging a small air gap in the flux path ofa strong magnet. The magnet is mounted on a cantilever supported leafspring, the end of the latter capable of being pushed downward bydepressing a key. When the key is depressed, the magnet moves downwardwith the spring and deflects the end of the reed. The reed breaks freewhen the restoring force in it exceeds the magnetic pull, and vibratesat its natural frequency. The magnet continues downward until it or thekey hits a stop. The small air gap assures that virtually no leakageflux will penetrate the reed after it breaks free of the magnet, so thatthe reed will vibrate at a constant single frequency. Releasing the keyenables the leaf spring to return to rest, the magnet moving up andagain attracting the reed to stop its vibration.

The invention may be more clearly understood by reference to thefollowing specification and the accompanying drawings in which:

Fig. l is a top view of a preferred embodiment of the invention;

Fig. 2 is a partially sectioned view in front elevation showing themagnet assembly;

Fig. 3 is a partially sectioned view in perspective of a telephone setshowing the invention assembled therein; and

Fig. 4 is a circuit schematic of a telephone set includ-y ing theinvention for tone dialing.

Referring now to the accompanying drawings, 2 is a mounting block ofnon-magnetic material such as brass within which the magnet assembly 4is housed and to which the cantilever supported leaf spring 6 and thecantilever supported reed 8 are afrlXed. The magnet assembly 4 comprisesa U-shaped soft magnetic element 10 the legs of which are secured to theleaf spring 6, a spacer 12 of non-magnetic material such as brass, and ablock 14 of magnetic material such as Alnico V securely positionedbetween the legs of the U-shaped element 10 and the spacer 12. A narrowgap 16 cut through the center of the U-shaped element defines thepole-pieces 18 and 20. Pole-pieces 18 and 2.0 project above the U-shapedelement.

The at leaf spring 6, made of a material such as Phos phor bronze, issupported horizontally in the mounting block 2, secured at one end 22and free to be deflected downward at its other end 24. The reed 8, madeof a magnetic mtaerial, is supported horizontally in the mounting block2 parallel to the leaf spring 6 and the lJ-shaped element of the magnetassembly. It is secured at one end and free to vibrate at the other endwhich bridges the air gap 16 and is held magnetically by polepieces 18and 20. The vibratory end has a contact 26 which, when the reedvibrates, closes to contact 28 affixed, as by soldering, to contactsupport member 30. Contact 28 may be in the form of a wire. Contactsupport member 3i) is free at the end which supports contact 28 andsecured at the other end to support member 42 by means of an insulatingspacer block 34.

In the embodiment shown in Figs. l and 2 reed 8 is in contact withpole-pieces 18 and 20 when bridging gap 16. While this arrangement hasbeen found to be satisfactory, frictional wear may be further minimizedby providing a thin spacer of relatively soft non-magnetic materialbetween reed 8 and pole-pieces 18 and 20.

When the leaf spring 6 is depressed, as by means of the key 36 (Fig. 3),the magnet is pushed down and pulls the reed 8 with it. When therestoring force set up in the reed exceeds the magnetic pull, the reedbreaks free and vibrates to make and break contacts 26 and 28 at thenatural frequency of vibration of the reed. The magnet continues to movedownward until the spring 6 hits the stop 38. When key 36 is releasedspring 6 returns to its rest position and reed 8 is reengaged by themagnet pole-pieces 18 and 20. As shown in Figs. l and 2 the free portionof reed 8, as determined by the cut 40 in block 2, establishes the reedsnatural frequency of vibration.

As shown in Figs. l, 3 and 4, the invention may be used to advantage inkey-operated frequency tone signaling telephone systems. In theembodiment shown in Figs. l and 3 five magnetic plucking units areassembled in a single block 2 and each unit is associated with anindividual key 36. Ten keys may be provided and assembled in such mannerthat each key will simultaneously pluck a particular combination of twoof the reeds. This can be accomplished by the use of a suitablemechanical linkage, whereby the depression of a key producessimultaneous motion of two of the plucking magnets, as taught in the artreferred to hereinbefo-re. Ten frequency combinations, corresponding tothe ten digits on a telephone dial, will thus be made available.

The schematic diagram in Fig. 4 shows a conventional telephone setequipped with the invention for key-operated tone dialing. The setincludes an equalizer 4?., which maintains substantially constant signallevel at the receiver regardless of differences in lengths of subscriberloops and limits the battery supply current through the transmitter, andan anti-sidetone network 44. On hearing dial tone the subscriberdepresses a key corresponding to the first digit to be dialed. Themovement of the key downward plucks the reed or reeds associated withthe key. The ssytem may be so arranged that the movement of the keydownward will also successively close a first Contact 46 whichshort-circuits the reeciver to prevent clicks when the set is removedfrom the line, and open a second contact 48 which removes the set fromthe line.

The use of a small air gap and the fact that the magnet is removed fromproximity to the reed when the reed is released makes damping of thereed motion by the magnetic field negligible. This results in theproduction of a very nearly pure resonant frequency tone. Since there isno Wear on the reed, uniformity of reed vibration is achieved and thefrequency remains the same in spite of repeated operation. The reed isplucked identically no matter how fast or how slow the subscriberdepresses the key.

It is to be understood that the above-described arrangements areillustrative of the application of the principles lof the invention.Other arrangements may be devised by those skilled in the art withoutdeparting from the spirit and scope of the invention.

What is claimed is:

1. A vibratory signaling device comprising a mounting member having anaperture, a iiexible, magnetic, cantilever reed secured to said mountingmember, the frec portion of said reed extending over said aperture, aiiexible cantilever spring member secured to said mounting member, amagnet disposed in said aperture between said reed and said springmember and mounted on the free portion of said spring member, saidmagnet comprising a C-shaped member and a pair of pole tips, said poletips projecting from said member and disposed between said member andsaid reed, said pole tips deiining a gap therebetween, the free end ofsaid reed bridging said gap to be held magnetically by said pole tips, acontact supporting member secured to said mounting member, a firstContact element affixed to the free end of said reed, a second contactelement aiiixed to said contact supporting member, said second contactelement being adapted to engage said first contact element, means fordisplacing said spring member beyond the position at which said reed issuddenly released from said magnet, said sudden release causing saidreed to vibrate and said first and second Contact elements to engage andseparate at the natural frequency of said reed, the natural frequency ofsaid reed being determined by the free portion thereof as determined bythe dimensions of said aperture.

2. A vibratory signaling device comprising a mounting block having aplurality of spaced apertures, a plurality of flexible cantilever springmembers secured to said mounting block in such manner that the freeportion of each of said spring members extends into an individual one ofsaid apertures, a plurality of flexible magnetic cantilever reedssecured to said mounting block in such manner that the free portion ofeach of said reeds extends over an individual one of said apertures,said reeds being substantially parallel to said corresponding springmembers,

an individual magnet disposed in each of said apertures betweencorresponding reed and spring members and mounted on the free portion ofits related spring member, said magnet comprising a C-shaped member anda pair of pole tips, said pole tips projecting from said member anddisposed between said member and its related reed, said pole tipsdefining a gap therebetween, the free end of its related reed bridgingsaid gap to be held magnetically by said pole tips, a separate Contactsupporting member secured to said mounting member substantially oppositeeach of said reeds, a first contact element affixed to the free end ofeach of said reeds, a second contact element affixed to each of saidcontact supporting members, each of said second contact elements beingadapted to engage its corresponding first Contact element, means fordisplacing each of said spring members beyond the position at which itsrelated reed is suddenly released from its magnet, said sudden releasecausing said reed to vibrate and said first and second contact elementsrelated thereto to engage and separate at the natural frequency of saidreed, the natural frequency of each of said reeds being determined bythe free portion thereof as deter'- mined by the dimensions of theaperture related thereto.

3. A vibratory signaling device in accordance with claim 2 wherein saidspring member displacing means is a manually operable key member.

4. A vibratory signaling device comprising a mounting block having aplurality of spaced apertures, a plurality of iiexible, magneticcantilever reeds secured to said mounting block, the free portion ofeach of said reeds extending over a separate one of said apertures, anindividual magnet disposed in each of said apertures between one of saidreeds and a supporting spring member secured at one end to said mountingblock and free at its other end to be deiiected downward, said magnetbeing secured to the free portion of said spring member and disposed insuch manner as to hold the free end of its related reed magnetically,said magnet comprising a C-shaped member and a pair of pole tips, saidpole tips projecting from said member and disposed between said memberand its related reed, said pole tips defining a gap therebetween, thefree end of its related reed bridging said gap to be held magneticallyby said pole tips, a separate contact supporting member secured to saidmounting member substantially opposite each of said reeds, a firstcontact element aiiixed to the free end of each of said reeds, a secondcontact element atlixed to each of said Contact sunporting members, eachof said second contact elements being adapted to engage itscorresponding first contact element, means for deiiecting each of saidspring members beyond the position at which its related reed is suddenlyreleased from its magnet, said sudden release causing said reed tovibrate and said first and second contact elements related thereto toengage and separate at the natural frequency of said reed, the naturalfrequency of each of said reeds being determined by the free portionthereof as determined by the dimensions of the aperture related thereto.

5. A vibratory signaling device in accordance with claim 4 wherein saidspring member deflecting means is a manually operable key member.

References Cited, in the tile of this patent UNITED STATES PATENTS Re.21,038 Leins Mar. 28, 1939 1,061,919 Miller May 13 ,1913 1,254,658Clausen Ian. 29, 1918 1,348,842 Barlow Aug. 10, 1920 1,643,270 GreinerSept. 20, 1927 2,269,242 Bakke Ian. 6, 1942 2,289,830 Ellwood July 14,1942 2,618,717 Westin Nov. 18, 1952 2,770,697 Kellett Nov. 13, 1956

